Many industrial processes require, as an integral step thereof, the identification of the color of one or more objects. One such example is the process of connecting a color-coded wire to a matching contact of a multi-contact electrical connector. While accurate color identification is essential if the proper wire is to be matched to the corresponding contact, manual color identification has often yielded inaccuracies due to operator boredom and eyestrain as well as difficulties in distinguishing small differences in hue.
An example of a proposal to automate color identification is disclosed in U.S. Pat. No. 4,278,538, issued July 14, 1981, in the name of H. S. Lawrence et al. and assigned to Western Electric Co. The Lawrence et al. system includes three photodetectors positioned to sense the intensity of the light reflected from an illuminated object, the color of which is to be identified. Filters are provided on each of a pair of photodetectors to make each of them sensitive to a separate one of two primary colors. The third photodetector is filtered so as to be sensitive to a color, which, when added to each of two primary ones, effectively synthesizes the third primary color. The output signals of the photodetectors are processed by a microprocessor to obtain a set of three values, each representative of the intensity of one of the three primary colors in the light reflected from the object. These intensity values are compared to separate sets of standard intensity values, each associated with a separate known color. When a substantial match is found between each of the three actual intensity values and the three intensity values of one standard set associated with a known color, then the color of the object will be known.
In order for Lawrence et al. to achieve repeatable, accurate color identification of an object, the color spectra of the lamp illuminating the object must be kept substantially constant. To this end, Lawrence et al. provide a feedback system for controlling the excitation of the lamp in accordance with the color spectra thereof. However, adjusting the excitation of the lamp to control its color will not compensate for variations in the output signal of each photodetector, which may be caused by the aging thereof or the presence of dirt on the filter in front of the detector. Such variations in the output signal of the detector may sometimes lead to erroneous color identification.